Not Applicable.
Not applicable.
1. Field of the Invention
The present invention relates to floating platforms used in the exploration and production of offshore minerals, and, more particularly, to a semisubmersible floating platform having a truss and air cans telescopingly mounted to the platform and movable between upper and lower positions with respect to the platform.
2. Description of the Prior Art
Prior floating platforms used in the exploration and production of offshore minerals are described in U.S. Pat. No. 4,702,321 to Edward E. Horton for xe2x80x9cDrilling, Production, and Oil Storage Caisson for Deep Water,xe2x80x9d U.S. Pat. No. 4,740,109 to Edward E. Horton for xe2x80x9cMultiple Tendon Compliant Tower Construction,xe2x80x9d and U.S. Pat. No. 5,558,467 to Edward E. Horton for xe2x80x9cDeep Water Offshore Apparatus.xe2x80x9d
A system with a guide frame for petroleum production risers is disclosed in PCT International Publication No. WO 00/58598 (Application No. PCT/NO 00/00106). A satellite separator platform is disclosed in PCT International Publication No. WO 00/63519 (Application No. PCT/US 00/10936).
The present invention provides a method of installation of a floating platform at a production location. The platform has a truss and riser buoyancy members telescopingly mounted therein. The riser buoyancy members are laterally restrained by guides attached to the truss. The method comprises towing the platform to the production location at a relatively shallow, towing depth with the truss and riser buoyancy members in a raised position within the platform. The method further comprises lowering the truss telescopingly to a lowered position extending below the platform. At least some of the guides laterally restrain the riser buoyancy members throughout the lowering process. The method further comprises lowering the riser buoyancy members telescopingly into the lowered truss. At least some of the guides laterally restrain the riser buoyancy members throughout this lowering process as well. The method further comprises installing risers through the riser buoyancy members for connection to wells on the sea floor.
According to a second aspect of the invention, a semisubmersible floating platform for use in marine environments is provided. The platform comprises a truss telescopingly mounted to the platform and movable between upper and lower positions with respect to the platform. At least one riser buoyancy member is telescopingly mounted to the platform and movable between upper and lower positions with respect to the platform. For each riser buoyancy member, at least one guide is attached to the truss and adjacent the buoyancy member for guiding and laterally restraining the buoyancy member.
According to a third aspect of the invention, a semisubmersible floating platform for use in marine environments is provided. The platform comprises a buoyant hull and a deck mounted to the hull. A truss is telescopingly mounted within the hull and movable between upper and lower positions with respect to the platform. A plurality of air cans are telescopingly mounted within the hull and movable between upper and lower positions with respect to the platform. The air cans are substantially caged by the truss when the truss and the air cans are in their raised and in their lowered positions with respect to the platform. The air cans are adapted to receive risers therethrough for providing buoyancy to the risers. For each air can, at least one guide is attached to the truss and adjacent the air can for guiding and laterally restraining the air can.